Header Files

The header files are located in the include/ directory. There are several sub-directories, each containing header files for different purposes. Three of these are available to plugins.


The C Plugin API. These call functions directly embedded in traffic_server and therefore have no explicit linkage.


The C++ Plugin API. These call functions in the libtscppapi.so library to directly interact with the running Traffic Server instance.


The C++ Plugin API is deprecated in ATS 10. It will be removed in ATS 11.


C++ utilities. These are standalone headers (although they may depend on other headers in the same directory). These provide functionality that is used inside the Traffic Server core logic but has been demonstrated to be useful for plugins as well [1]. The functions are in the library libtsutil.so, although many of the utilities are header only. This library is linked in to the traffic_server binary and so linkage may not be needed for a plugin.

This library is independent of the C++ API and can be used with or without that library.


Traffic Server core header files. These can only be used inside Traffic Server itself because they either depend on internal data structures either directly or operationally. This is linked in to the traffic_server binary therefore has no explicit linkage when used in the core.

New Plugin API layout

Previously, all plugin interfaces were built into the main Traffic Server binary. In an effort to enhance modularity and enable compile-time checks, these interfaces have been moved to src/api. They are now isolated into a separate shared library tsapi.so.

In addition, a new static library tsutil.a has been created, which contains code used by both the core and the plugins (via the plugin APIs), and is linked into the Traffic Server binary to keep functionalities consistent.

Note that tsapi.so depends on tsutil.a and other static libraries in the core. tsapi.so is not statically linked against these dependencies during its creation, but relies on them being linked into Traffic Server. To verify these dependencies, a compile-time sanity check links tsapi.so with the main Traffic Server binary (Traffic Server), ensuring all symbols required by tsapi.so will be available in Traffic Server. The actual binding of these dependent symbols occurs dynamically at runtime when Traffic Server is launched.


This was a major restructuring the source code layout. The primary goal of this was to unify the include paths for the core and plugins for these headers, and to make C++ support code used in the core also available to plugins. Previously plugins in the Traffic Server codebase used these headers because they could reach over and include them, but third party plugins could not because the headers were not installed.

“proxy/api/ts” was moved to “include/ts”, along with a couple headers from “lib/ts”. This consolidates the C plugin API.

The C++ API headers were split from the source and moved to “include/tscpp/api”. The source files were moved to “src/tscpp/api”.

The contents of “lib/ts” were broken up and moved to different locations. The headers were moved to “include/tscore” for core only headers, while headers to be made available to plugins were moved to “include/tscpp/util”. The corresponding source files were moved to “src/tscore” and “src/tscpp/util” respectively. “libtsutil” was split in to “libtscore” for the core code and “libtscpputil” for shared code. Now “libtscpputil” has been combined with “tsapicore” headers into the “tsutil” library.